Stair system with adjustable width

ABSTRACT

A stairway assembly having an external step portion, an internal step portion slidably engaged with the external step portion; a first stringer secured to the external step portion to support the external step portion; and a second stringer secured to the internal step portion to support the internal step portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent application Ser. No. 11/168,208, entitled “STAIR SYSTEM WITH EXPANDABLE CENTER,” which was filed on 28 Jun. 2005, and is currently pending. That application relies on priority from U.S. Provisional Application Ser. No. 60/583,203, which was filed on 28 Jun. 2004. The contents of all applications are incorporated herein by reference.

STATEMENT REGARDING COPYRIGHTED MATERIAL

Portions of the disclosure of this patent document may contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office file or records, but otherwise reserves all copyright rights whatsoever.

FIELD OF INVENTION

This invention generally relates to a staircase system, more specifically to an adjustable staircase system and, still more precisely to a staircase system that slides widthwise to adjust to different width staircases. This may also be known as a staircase system with an expandable center that is easily and quickly built, cost effective and is safe to be installed by an average worker.

BACKGROUND OF THE INVENTION

A major cost portion of any construction project, whether residential, commercial, or industrial, is that of stair construction. The specialized nature of stair construction, coupled with the multitude of individual pieces that may fit exactly, various building codes that may be met and the various materials that can be used, make it necessary to use highly skilled craftsmen to design and construct stairs. These craftsmen are necessary whether building one stair or multiple stairs of the same design, because of the small variations between floor heights, and floors may lead to a not so perfectly level or square. Accordingly, the need has arisen, for the development of the Stair System which provides the flexibility of expansion in height and length and at a low material and labor cost.

U.S. Pat. No. 5,890,330 discusses an adjustable staircase system; where adjustable steps extend between two parallel stringboards. Each stringboard includes two locking flanges and each step is supported by four pivotable blocks each securable to a flange by means of a nut. Two threaded rods extending through the step and between the stringboards engage two respective nuts combined with two opposite blocks. The height of each step of the staircase may be adjusted by changing the spacing between the blocks along each flange. The horizontal position of the steps may be adjusted by changing the vertical distance between the front blocks and rear blocks along the stringboards, regardless of the angle at which the stringboards were fitted. A universal staircase may thus be achieved. Considering various aspects this system is limited in many ways as pivotable blocks make the assembly bulky and costly without added benefit adding towards extra installation time.

In another U.S. Pat. No. 5,636,483 a system is discussed where a prefabricated stair system having individually pivotally mounted right angular brackets on opposed stringers, has a control bar which removable contacts the brackets to assume all brackets are arranged at the same angles with respect to the stringer so that the treads, which are supported by opposed pairs of brackets, are parallel to the floors and the risers supported by the brackets are perpendicular to the treads. The stair system is shipped as a kit and assembled in situ following a method of assembly and installation. This system as the system is made to order and thus limited in its scope in various ways and having many components making the assembly complicated and time consuming for installation. U.S. Pat. No. 3,914,912 discloses a stairway that uses fabrication that uses treads and risers secured at right angles. Fasteners extend from each side into notches in the stringers. The stairs are then installed by installing each riser and tread to the stringers by positioning the fasteners into the notches.

The above mentioned prior arts and some other related works are either expensive or cumbersome for assembly and require highly skilled craftsman to design and construct stairs and thus they are time consuming in construction and increasing the labor cost as well. So there is a need for a low cost and a simple adjustable staircase system which can be installed quickly by an average worker providing more strength to all the stair treads. There is no stairway that has two slidable portions to adjust to the width of varying stairways.

OBJECT OF THE INVENTION

In view of the foregoing disadvantages inherent in the above-mentioned techniques, a general object of the present invention is to obviate above and other drawbacks associated with the prior art.

The object of the invention is to provide with a staircase system.

It is further object of the present invention to provide with an adjustable staircase system.

Another object of the present invention is to reduce the assembling complexity of the system.

It is yet another object of the present invention to make the system cost effective.

Still another object of this invention is to reduce the required installation time.

It is still another object of the invention to provide with an attachment of a temporary handrail.

SUMMARY OF THE INVENTION

One aspect of the present invention is a staircase assembly comprising: a plurality of stringers having a series of substantially equally spaced substantially vertical structure notched out of one side to define the height of each step of the stair system, and a series of substantially equally spaced substantially horizontal structure notched out of one side to define the length of each step of the stair system; a central stringer disposed between at least two other stringers; a substantially vertically oriented riser; a substantially horizontally oriented tread that extends horizontally from a lower end of said vertically oriented riser to form a step at the lower end of the riser, and to define a riser and tread boundary; a rounded extension piece offset from said riser and tread boundary; a different riser having a receiving groove portion that is capable of receiving said rounded extension piece to define a stair unit; and a plurality of stair units, having a substantially vertically oriented riser and a substantially horizontally oriented tread; whereby the stairs can be adjusted laterally via lateral sliding between the receiving groove and the first projecting structure. The staircase assembly may comprise a plurality of stringers, and; a plurality of stair units, having treads and risers wherein stair unit is secured by means of fastening means on each corner to said plurality of stringers.

Another aspect is a stairway assembly comprising: an external step portion (500); an internal step portion (600) slidably engaged with said external step portion (500); a first stringer (790) secured to said external step portion (500) to support said external step portion (500); and a second stringer (750) secured to said internal step portion (600) to support said internal step portion (600). Said stringers, having a diagonally shaped series of equally spaced substantially vertical structure notched out of one side to define the length and height of each step of the stair assembly.

The said tread, forming a channel by rolling the leading edge for holding the riser of the stair unit installed immediately below, and each stair unit is secured by means of fastening means on each corner to said plurality of stringers, said channels further engaging other stair unit laterally sliding for providing horizontal adjustability.

A staircase assembly further comprising tread having catching holes at a predetermined distance that is identified according to the length of the staircase, and a handrail assembly having a handrail posts, securing means, and rails, handrail post designed for fixing to the holder of said stringers through the catching holes of said treads and securing means are configured for clamping this assembly tightly to said stringers.

According to the another aspect of the invention an adjustable staircase assembly having a plurality of stairs each stair having a base unit having a receiving grove at its angled corner, and a stair unit having a first projecting structure, a curved structure and a second projecting structure, for fixing on top of said base unit, characterized in that the said first projecting structure is configured for fixing it into the said receiving grove of the base unit, and the curved structure is configured for clamping the said second projecting structure of a second stair to form a staircase assembly.

The invention described herein is not limited to above description, any other embodiment implementing the concept of instant invention will fall under the scope of the present invention and will be the subject matter of the protection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the stair system with expandable center;

FIG. 2 is an inside or left-hand view of the stair system with expandable center with an exploded view of the bottom stair unit showing greater detail, according to a preferred embodiment of the present invention;

FIG. 3 is an opposing perspective view of the stair system with expandable center, with an exploded view of the bottom stair unit showing greater detail;

FIG. 4 is a piecemeal view of the stair system with expandable center, prior to final installation;

FIG. 5 is a perspective view of a stair unit;

FIG. 6 is a side view of a stair and base unit attached together, according to an alternate embodiment of the present invention;

FIG. 7 is a side view on one embodiment of a stair and base unit attached together;

FIG. 8 is a side sectional view of a plurality of external and internal stair portions, to form a set of steps;

FIG. 9 is a pictorial of one embodiment of the present invention with the external stair portion and the internal stair portion relatively close in displacement;

FIG. 10 is a pictorial of one embodiment of the present invention with the external stair portion and the internal stair portion displaced from one another, as compared with the configuration as illustrated in FIG. 9;

FIG. 11 is a pictorial of a view showing the external step portion 500 and internal step portion 600 of one embodiment of the present invention

FIG. 12 is a side view of one embodiment;

FIG. 13 is a front view of one embodiment; and

FIG. 14 is a top view of one embodiment.

REFERENCE NUMERALS

-   20 outer stringer -   25 central stringer -   31 riser -   32 tread -   33 corner bend -   34 lip -   35 bolt hole -   36 handrail aperture -   37 lap seam -   41 handrail post -   42 post receptacle -   43 bracket -   44 handrail system -   46 first projecting structure -   48 receiving grove -   50 second projecting structure -   310 internal riser -   312 external riser -   320 external runner -   325 external junction -   340 internal runner -   400 first side -   410 second side -   420 third side -   430 fourth side -   440 lip -   480 interface -   490 groove -   500 external step portion -   600 internal step portion -   700 structure -   750 second stringer -   770 central stringer -   790 first stringer

DETAILED DESCRIPTION OF THE DRAWINGS

A further understanding of the present invention may be obtained with reference to the following description taken in conjunction with the accompanying drawings. However, the embodiments used for describing the invention are illustrative only and no way limiting scope of the invention. A person skilled in the art will appreciate that many more embodiments of the invention are possible without deviating from the basic concept of the invention any such embodiment will fall under the scope of the invention and is a subject matter of protection.

FIG. 1 is a perspective view of the stair system with expandable center shown as a complete built system of its components.

FIG. 2 shows the left-hand side view of the stair system where DETAIL A shows the configuration of the individual stair units and their relationship to each other.

FIG. 3 is a front perspective view of the stair system and illustrates the sliding engagement between two individual stair units and the corner bent 33 so created. DETAIL B provides greater detail of the attachment point of the handrail system 44, specifically the handrail post 41 secured within the post receptacle 42. The handrail system 44 comprises handrail posts 41, brackets 43, and rails and is generally tubular on shape and lightweight, yet resilient in construction. The post receptacle 40 is designed to receive the handrail post 41 and is cylindrical is shape with one open end and means to lock the handrail post 41 in place. The inner diameter of the receptacle 42 is slightly larger than that of the handrail post 41 and is constructed of similar materials. A bracket 43 is affixed to the inner wall surface of the right-hand stringer 20 to retain the post receptacle 42 to said stringer 20.

FIG. 4 shows the stringer boards 20, 25 that are typically a diagonal-shaped device with a series of 90° angles notched out of one side to define the length and height of the tread 32 and riser 31 portions of the stair system. The stringer boards 20, 25 should all be of equal shape and size and utilize conventional mechanical fasteners when installed to the building framework.

FIG. 5 shows the stair units should all be of equal shape and size. The stair unit is bent at a 90° angle making a corner bend 33 which defines the tread 32 and riser 31 to match that of the tread and riser cut-outs on the stringers 20, 25. The leading edge of the tread 32 is formed into a lip 34, or “C”-channel which doubles back against itself to a point upon which the clearance between the lip 34 and the riser 31 portion of the stair unit installed immediately below. The lip 34, of individual stair units 34 are designed to sliding engage each other laterally, thereby defining a left- and right-hand stair unit. Both left-hand and right-hand stair units have bolts holes 35 drilled there through on the left side and right side, respectively for affixing the stair unit to its respective stringer 20. The right-hand stair units also have an aperture 36 drilled there through at the bottom, top, and every seventh or central stair unit to accommodate the handrail system 44.

FIG. 6 illustrates an alternate embodiment of the stair system. The stair assemblies here include two separate units, riser 31 and a tread 32, a retaining clip to connect two stair units together, and a sliding assist piece. DETAILS A and DETAILS B show the bends and configuration for the riser and stringer, as well as the shapes of the second projecting structure 50 and lip 34. The material of construction for the base and stair unit may be the same as is shown in FIG. 5 and the retaining clip and sliding assist piece for vibration dampening and minimal friction may be an ultra-high molecular weight (UHMW) polyethylene or other material with the same properties. DETAILS A and B show the bends and configuration for the stair and base units, as well as the shapes of the retaining clip and sliding assist piece.

The preferred embodiment of the present invention is designed to be used by a normal person with some skills and minimal training necessary.

The stair system with expandable center 10 is designed for the fabricator or building contractor in mind. Custom building flights of stairs can take a lot of time that could be used to complete other tasks. Therefore, a reliable and easily constructed modular stair system that can fit any situation such as is presently defined can become a great time and resource saver.

The present invention is designed to be pre-fabricated off-site according to the general specifications of the construction and transported to the site for final fitting and finishing in the space provided. The first step is measuring the total height and width by laying out the rise and run of the stringers 20, 25 that will be cut. The height is determined by the measured distance between the finished bottom floor to the top of the upper deck and the width is generally determined by standard building codes. Two (2) outside stringers 20 and a third central stringer 25 are identically cut to form the support structure of the stair units 30.

The next step required is to form the tread 32 and riser 31 from the sheet stock of the stair unit 30 to the required shape. A 90° angle is needed to define the boundary 33 of the tread 32 to the riser 31. On the opposite end of the tread 32 from the bend 33, a lip 34 is formed by rolling the leading edge about a radius and doubling back against itself creating a “C”-shaped channel, through which another stair unit 30 similarly formed can slide therethrough. The backwards bend of the lip 34 should result in minimal clearance between the lip 34 and the front-facing surface of the top of the riser section 31 of the bottom stair unit 30. Apertures or slots 35 are then formed at spaced intervals near the same edge of the tread 32 and riser 31 to accommodate nails or bolts. Care must be taken here to form identical stair units 30. Half of the stair units 30 should have the formed bolt holes 35 on its right side (see FIG. 5) and the other stair units' bolt holes 35 formed on the left side. Also, the handrail pole aperture 36 is cut out on a desired side of the tread 32 of every seventh stair unit 30 guidelines (see FIG. 5), and ensuring that the bottom, top, and at least one central stair unit 30 are included.

At this point, the finished stair units 30 should be secured to the top and front surface of the stringers 20, 25. Handrail pole receptacles 42 are mounted on brackets 43 are to be installed on the inside surface of the stringer 20 at locations corresponding to the bottom step, top step, and seventh or central step at a position below the projected placement of the stair unit 30 (see FIG. 3, Detail B). Edge and pressure blocking may at this time be attached at the top and bottom of each stringer 20 for use during final installation. The pre-fabrication of the stair system with expandable center 10 is now ready for transport to the job-site, along with the central stringer 25 and handrail system 44.

When the pre-fabricated stair system 10 has been delivered to the job site and placed in the space provided, final installation of the device 10 should commence (see FIG. 4). The right and left sides of the system 10 are adjoined together by overlapping the “C”-channels 34 of the treads 32 of one side overtop the other side, providing a sliding engagement between the two (2) sides. It is important at this stage to ensure that the side with the temporary handrail pole apertures 36 are on the outside edge as opposed to abutment of the stair system 10 against a wall. One side of the stair system 10 should be secured to the building framework with the other side manipulated into place by sliding the entire side until it abuts the framework on the opposite side, at which point it is secured thereto. The central stringer 25 is then secured at a central point underneath the stair system 10 by bolts, screws, or nails driven through the tread 32 and riser 31 portions of the overlapping stair units 30, preferably in the same pattern as used to secure the separate stair units 30 to their respective stringer 20. Any height adjustment is inherently minimal due to building code regulations on riser 31 height and are accounted for by the overlap and bend of the lip 34 formed at the leading edge of the tread 32 portion (“C”-channel) during pre-fabrication.

The handrail system 44 is then installed where needed by feeding the poles 41 through the apertures 36 located on the tread 32 and secured within the receptacle 42 mounted to the inside of the stringer 20 via a bracket 43 by a channel lock or similar system. A similar securing system is present for installing the handrails to the pole 41. Both the handrails and poles 41 may be expandable as necessary. This handrail system 44 is necessary due to OSHA requirements and may be easily removed and the apertures 56 covered with a cap or plug when the handrail system 44 is not installed.

Additional finishing for the handrail system 10 is generally left up to the building fabricator or stair constructor but typically involves the use of an adhesive or coating to protect the stair system 10 and to cover, protect, and level the lap seam 37 formed during final installation. It is conceived that an adhesive tape will be applied to the lap seam 37 to effect a smooth transition for carpet applications. Edge and pressure blocking for final construction may be attached during pre-fabrication or during final installation.

It is conceivable that other alternate embodiments for the present invention may provide additional support and ease of construction. A “T”-channel piece designed for attachment directly to the top surface of each stringer step, with the extended piece fitting within a similarly shaped and sized notch formed downward from the top surface of said stringer step, provides added support for the stair units.

A more elaborate design involving a separate tread and riser stair unit and base unit with more bends are referred to in FIG. 6. The sliding point in particular has a separate rounded extension piece offset from the corner bend defining the riser and tread boundary and running the entire width of said boundary. This rounded piece is received within a similarly yet opposite shaped groove on the base unit. The base unit is placed first on top of the top and front facing stringer surfaces and the tread and riser stair unit is placed on top of the base unit, with the vertically interlocking pieces corresponding to specialized bends at the leading edge of the tread portion. Vibration dampening devices such as UHMW polyethylene fill in the space and secure said stair units and base units together at the lip joint and at the sliding point to provide a smoother movement between the lateral stair units.

In one embodiment of the present invention, as illustrated in FIG. 7, an internal riser 310 may be oriented substantially vertical, and an internal runner 340 that may be oriented substantially horizontal. The internal riser 310 extends downwardly, and the internal runner 340 extends horizontally in the direction of the internal riser 310 to form an interface 480 having a groove 490. The groove 490 is capable of receiving a tongue 460.

As illustrated in FIG. 8, the interface 480 may be bulbous interface 480, or it may be a substantially flat interface 485. Accordingly an external riser 320 is oriented substantially vertical, and an external runner 330 is oriented substantially horizontal. The external runner 330 and external riser 320 meet to form an external junction 325.

As illustrated in FIG. 8, a first side 400 is exposed on the external riser 312 and external runner 320. A second side 410 is the side 410 of the external riser 312 and external runner 320 that faces the internal riser 310 and internal runner 340. A third side 420 identifies the surface of the internal riser 310 and internal runner 340 that faces the second side 410. A fourth side 430 identifies the surface of the internal riser 310 and internal runner 340 that is opposite of the third side 420.

The external riser 312 and external runner 320 combine to form what is identified as the external step portion 500. The internal riser 310 and internal runner 340 combine to form what is identified as an internal step portion 600. The external step portion 500 is capable of sliding with respect to the internal step portion 600 via the tongue 460 and groove 490 arrangement. The function of the tongue 460 and groove 490 arrangement is to keep the external step portion 500 in some slidably proximal relationship with respect to the internal step portion 600. Other means to maintain the external step portion 500 in slidable engagement with the internal step portion 600.

FIG. 9 illustrates the stairs with the external step portion 500 and internal step portion 600 in one relational position. FIG. 10 illustrates the external step portion 500 and internal step portion 600 displaced or slid away from each other, and disposed in a different relational position from that illustrated in FIG. 9. As is illustrated the external step portion 500 and internal step portion 600 may be slidably connected. The smooth surface of the step portions 500, 600 allow for easily slidability of the portions. As shown in FIG. 9, the external step portion 500 may be secured to a first stringer 790, the internal step portion 600 may be secured to a second stringer 750. As illustrated in FIG. 10, when the step portions 500, 600 are slid out a central stringer 770 may be disposed between the first stringer 790 and the second stringer 750. Further, the internal step portion 600 may have a slightly shorter rise and run, so that the internal step portion 600 may slide inside of the external step portion 500.

FIG. 11 illustrates another embodiment of the present invention. In this embodiment the external step portion 500 and internal step portion 600 do not employ any tongue 460 and groove 490 arrangement. The external step portion 500 is the same shape as the internal step portion 600. One difference is that the external riser 320 and external runner 330 are each slightly longer than the internal riser 310 and internal runner 340 respectively, so that the external step portion 500 can fit externally or outside of the internal step portion 600. Although FIGS. 11-14 may refer to the external step portion 500 in the drawings, these features are similar is shape to the internal step portion 600. As the internal step portion 600 is slidably engaged with the external step portion. As illustrated in both FIGS. 11 and 12, the external runner 320 and internal runner 340 both may extend to a downwardly extending arm 442, and a horizontally extending finger 441 to form a C-shaped channel, which may allow for the internal step portion 600 and the external step portion to become slidably engaged.

As illustrated in FIG. 12, the internal step portion 600 may be secured to a structure, such as a stringer, such as an outer stringer 20, or central stringer 25. And each external step portion 500 may have a lip portion 440 formed contiguous with said external runner 320.

FIG. 13 illustrates a front view of an external step portion 500. In one embodiment, the external step portion may have bolt holes 35 to secure the external step portion 500 to a stringer. In one embodiment, the bolt holes 35 may be disposed about 0.75 inches from an edge.

FIG. 14 illustrates a top view of an external step portion 500. In one embodiment, the external step portion may have bolt holes to secure the external step portion 500 to a stringer. Further, the external step portion 500 may have a handrail aperture 36 disposed in the external runner 320 so that a handrail may be disposed therethrough.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 

1. A staircase assembly comprising: a plurality of stringers having a series of substantially equally spaced substantially vertical structure notched out of one side to define the height of each step of the stair system, and a series of substantially equally spaced substantially horizontal structure notched out of one side to define the length of each step of the stair system; a central stringer disposed between at least two other stringers; a substantially vertically oriented riser; a substantially horizontally oriented tread that extends horizontally from a lower end of said vertically oriented riser to form a step at the lower end of the riser, and to define a riser and tread boundary; a rounded extension piece offset from said riser and tread boundary; a different riser having a receiving groove portion that is capable of receiving said rounded extension piece to define a stair unit; and a plurality of stair units, having a substantially vertically oriented riser and a substantially horizontally oriented tread; whereby the stairs can be adjusted laterally via lateral sliding between the receiving groove and the first projecting structure.
 2. A staircase assembly as defined in claim 1 wherein said assembly further comprising said substantially horizontally oriented tread and said substantially vertically oriented riser having bolt holes therein a handrail post; said substantially vertically oriented riser having a handrail aperture therein, said handrail aperture capable of receiving said handrail post; whereby said substantially horizontally oriented treads and said substantially vertically oriented risers are secured to said stringers by bolting said treads to said stringers via said bolt holes.
 3. A staircase assembly as defined in claim 1, wherein said substantially vertically oriented riser having a jutting projection for holding said tread of immediate upper stair unit.
 4. An adjustable staircase assembly as defined in claim 1, wherein said assembly further comprising an adjustable central support frame for supporting said treads.
 5. An adjustable staircase system as defined in claim 1, wherein said assembly has a railing.
 6. A staircase assembly comprising: a plurality of stringers having a series of substantially equally spaced substantially vertical structure notched out of one side to define the height of each step of the stair system, and a series of substantially equally spaced substantially horizontal structure notched out of one side to define the length of each step of the stair system; a central stringer disposed between at least two other stringers; a riser having a vertical portion and a horizontal portion, and a receiving groove disposed therebetween; a tread having a vertical portion and a horizontal portion; and a first projecting structure extending away from said tread; said first projecting structure capable of being received within said receiving groove; said tread extends substantially horizontally away from said first projecting structure to form a lip; and a plurality of stair units, having said riser and said tread; whereby the stairs can be adjusted laterally via lateral sliding via the receiving groove and the first projecting structure.
 7. A staircase assembly as defined in claim 6 wherein said assembly further comprising said tread and said riser having bolt holes therein said riser having a handrail aperture therein, said handrail aperture capable of receiving said handrail post; whereby said treads and said risers are secured to said stringers by fastening said treads to said stringers via said bolt holes.
 8. A staircase assembly as defined in claim 6, wherein said riser having a jutting projection for holding said tread of immediate upper stair unit.
 9. An adjustable staircase assembly as defined in claim 6, wherein said assembly further comprising an adjustable central support frame for supporting said treads.
 10. An adjustable staircase system as defined in claim 6, wherein said assembly has a railing.
 11. A stairway assembly comprising: an external step portion (500); an internal step portion (600) slidably engaged with said external step portion (500); a first stringer (790) secured to said external step portion (500) to support said external step portion (500); and a second stringer (750) secured to said internal step portion (600) to support said internal step portion (600).
 12. The apparatus of claim 11, further comprising: a central stringer (770) secured to said internal step portion (600) to support said internal step portion (600), said central stringer (770) disposed between said first stringer (790) and said second stringer (750).
 13. The apparatus of claim 11, wherein said external step portion (500) further comprises: an external riser (312) oriented substantially vertical, and extending substantially from said external riser (312) is an external runner (320) oriented substantially horizontal to form a step; as said external runner (320) extends away from said external riser (312), said external runner (320) forms a downward curving lip (440).
 14. The apparatus of claim 13, wherein said downward curving lip (440) is in slidable engagement with an internal step portion downward curving lip (540).
 15. The apparatus of claim 11 wherein said external step portion (500) and said internal step portion (600) are each about 33 inches in width, and thus can slidably engage to a stairwell that is about 66 inches in width.
 16. The apparatus of claim 13 wherein the downward curving lip (440) has an arm (442) that extends downwardly to a finger (441) that extends substantially horizontal to form a C-shape with said external runner (320)
 17. The apparatus of claim 16, wherein said external runner (320) is about 11.5 inches, and said arm (442) is about 1.75 inches, and said finger (441) is about 1 inch. 